TROOP SHIPS TO INDIA 1800s

TROOP SHIPS TO INDIA 1800s

How would I find out about how troops with the British Army sailed to India in the mid 1800s? My grt grt grandfather was stationed in Ireland, married a local girl and was sent to India with his regiment. They eventually returned to Ireland - Belturbet, Co Cavan. I have no idea of where they were in India. Thanks for any help.